Conventionally, a heat exchanger formed of tubes and fins is generally used. For aiming at compactness, recently, the tube diameter and tube pitch have been decreased, and the tube density has been increased. For example, a heat exchanging section is formed of extremely thin tubes of which outer diameter is about 0.5 mm.
FIG. 27 is a front view of a conventional heat exchanger disclosed in Japanese Patent Unexamined Publication No. 2001-116481. In the conventional heat exchanger, inlet tank 31 and outlet tank 32 are faced to each other at a predetermined interval as shown in FIG. 27. Core section 34 is formed between inlet tank 31 and outlet tank 32, and, in core section 34, a plurality of tubes 33 with annular cross section are disposed and external fluid flows outside tubes 33.
Tubes 33 are arranged in a square grid shape, the outer diameter of tubes 33 is set between 0.2 mm and 0.8 mm inclusive, and the value derived by dividing the pitch between adjacent tubes 33 by the outer diameter is set between 0.5 and 3.5 inclusive. Thus, the heat exchange amount per working power can be significantly increased.
The specific elements and manufacturing method of the conventional heat exchanger are not described. In a generally considered method, however, many thin tubes 33 are prepared, inlet tank 31 and outlet tank 32 of which specific surfaces previously have many small circular holes are prepared, the opposite ends of tubes 33 are inserted into the circular holes in inlet tank 31 and outlet tank 32, and the inserted parts of tubes 33 are bonded to inlet tank 31 and outlet tank 32 by welding or the like. However, for manufacturing the thin circular tubes, a precise processing device is required, and hence the heat exchanger becomes expensive. Further, small circular holes into which tubes 33 are inserted must be disposed in inlet tank 31 and outlet tank 32 at a predetermined fine pitch, and hence it is difficult to perform a process of inserting and bonding tubes 33 to inlet tank 31 and outlet tank 32. Therefore, even when the heat exchanging performance of such a heat exchanger is high, the heat exchanger is extremely expensive, the reliability against the leak of the used fluid is not sufficient, and hence problems remain.
The present invention addresses the conventional problems, and provides a heat exchanger that keeps extremely high heat exchanging performance, has an easy-to-manufacture structure, is inexpensive, and has high reliability.